Electron image correlation tube with dual storage screens



Jan. 21, 1969 w, s R 3,423,624

ELECTRON IMAGE CORRELATION TUBE WITH DUAL STORAGE SCREENS Filed June 8, 1966 Sheet of 2 281 52' FOCUSING MLTAGE CONTROL FOR ALL TUBE ELEcTRooEQ CIRCUIT 48 7] IL/ 7;I-- -4a 38 m. I; 7 I2 [8 My DISCRIM- 36 'fia /32 INATOR Z4 /1 /I is I i FOR WRITING VIDEO FOR NUTATIONDISPLACE- SIGNALS INTO TUBEK/ MENT TO MATCH 55 RASTER DEFLECTION NUTATION GENERATOR CIRCUITRY GENERATOR X ERROR SIGNALS 'NTEGRATOR 28A? 52A? FOCUSING Mums CONTROL FOR ALL TUBE ELECTRODE] w cmcurr I L\ \\\\\\aoA/ 48A'M/ 7| [7 L4 I .j 2A 44A7 24A ,V/ZOA 26A PHAS 36A m1 I '9 v w 46A? E I I U 32A ZZAA/ DISCRIM- 4 INATOR .a4A aaA ISA Z/ 7r L\\\ W RASTER DEFLECTION MUTATION GENERATOR M- CIRCUITRY GENERATO INTEGRATOR ERROR SIGNALS INVENTOR W/LFORD L. STE/IVER A TTOR/VEY Jam. 21, 1969 w, L. TEINER 3,423,624

ELECTRON IMAGE CORRELATION TUBE WITH DUAL STORAGE SCREENS Filed June 8, 1966 Sheet 2 of 2 42 READOUT ANODE 22 GRID NO. 2

20 GRID NO. I

l8 PHOTO ELECTRON PATTERN CATHODE FOCUSED NUTATED BETWEEN THE GRIDS LIGHT SOURCE [NI/EN TOR W/L FORD L. STE/IVER A TTOR/VEY 8 Claims ABSTRACT OF THE DISCLOSURE An electronic image correlation tube with dual storage screens which utilizes structure to obtain a total flood of electrons down the tube towards the screens to achieve the correlation function when electron images have been stored on the screens in the conventional manner. An ultra-violet radiation source is utilized in conjunction with an area cathode to obtain the total electron flood.

This invention relates to an electronic image correlation tube which combines two separate storage grids to provide extended versatility in the application of electronic area correlation.

This invention represents an improvement in the art of image correlation Within a single tube, such as set forth in US. patent applicaton Ser. Nos. 232,961 now Patent No. 3,290,546 424,439 and US. Patent 3,194,511 also assigned to Goodyear Aerospace Corporation.

The general object of the invention is to provide an image correlation tube which utilizes two image storage screens whereby a reference image and a present image can both be stored independently with subsequent correlation between the two images then taking place as selectively desired to provide an operational capability heretofore not possible and more versatility to the equipment.

The objects of the invention are achieved by providing in a. dual image storage tube the combination of an elongated tubular-shaped housing or envelope, a pair of electron image storage screens mounted in spaced parallel relation within the housing, means to direct a scanning beam of electrons representing image information in the housing towards the storage screens, means to independently control the voltage on the screens whereby the electrons can pass through one screen and store the information on the other, and after a reference image has been stored on the other screen to then store information as a present image on the one screen, means to flood the one screen with a constant uniform area stream of electrons after images have been stored on each screen whereby the one screen space modulates the stream to produce an electron image of the information stored on the first screen, means to nutate the electron image stream between the storage screens, and means to detect the number of electrons of the nutated electron image stream passing through the other storage screen to achieve the correlation function between the images stored on the storage screens.

For a better understanding of the invention reference should be had to the accompanying drawings wherein;

FIGURE 1 is a block diagram schematic illustration of a preferred embodiment of the improved electron image correlator tube of the invention; and

FIGURE 2 is a slightly modified correlator tube also capable of meeting the objects of the invention; and

FIGURE 3 is a perspective schematic illustration of how area transfer or correlation is accomplished.

With reference to the form of the invention illustrated in FIGURE 1 of the drawings, the numeral indicates nited States Patent Ofice 3,423,624 Patented Jan. 21, 1969 generally an image matching system. The heart of the system is a special electron tube, hereinafter called a dual storage grid electron image correlation tube, and generally indicated by numeral 12. The tube 12 consists of a single housing or envelope 14 which is normally glass or ceramic and cylindrically shaped. The envelope 14 has a transparent end section 16 on one end thereof which has a photoemissive cathode surface 18 over the full inner surface thereof, as indicated. The image storage elements of the tube 12 comprise separate substantially fiat storage grid 20 and 22 positioned in spaced parallel relationship from each other and from the photo cathode surface 18. Each grid 20 and 22 also has a collector electrode 24 and 26 mounted therein in substantially spaced parallel relationship towards the photoemissive cathode, as indicated, to collect secondary emission electrons as more fully-identified applications. Focus circuitry 28 controls a current to focus coil 30 to produce a magnetic field which focuses all the electrons emitted from the photo cathode surface 18 onto either of the respective grids 20 and 22. In order to provide acceleration of the electron streams passing down the tube 14, a field mesh 32 is mounted in spaced parallel relationship to the photo cathode 18 and also to the storage grid 20. Also, suitable electron multipliers 33, well known in the art, may be positioned between the grid 22 and an output anode 42 so as to amplify the output signal.

In order to provide image information, either present or reference, the invention contemplates the incorporation of an electron gun 34 for writing the image information onto the storage grids by raster-scanning the videomodulated beam over the storage grids. A raster generator 55 controls the deflection of the electron beam to properly scan the input video signals, as is well known in the art. The image information is thus stored on the respective grids 20 and 22, as more fully defined below. Further, the invention contemplates the use of a lens 38 to receive any suitable optical input image 40 for conversion by the photo cathode 18 into an electron image to be focused by solenoid 30, driven with an appropriate current controlled by focus circuitry 28, onto either of the respective grids 20 and 22, as selectively desired, and more fully defined below.

It is important to note that the storage grids 20 and 22 are substantially perpendicular to the electron stream, and are located so that the electronic image generated by the scanning beam from the electron .gun 34 may be focused on either storage grid, as hereinafter described, and so that an electron image of the information stored on the first storage grid when reconstituted by the flood beam may be focused on the second storage grid. As shown in the drawings, FIGURE 3 rather clearly illustrates the use of a flood beam, or a total uniform illumination of the photo cathode 18 to uniformly flood the first grid 20, which has a previously stored electronic charge pattern thereon. The charge pattern then space modulates the flood beam to effectively transmit the charge pattern onto the second grid 22. Any discrepancy between the transmitted charge pattern and that stored on the grid 22 is detected by the passage of electrons therethrough collected by the output anode 42.

In order to detect correlation information, conducting output anode 42 is located a suitable distance beyond the second storage grid to collect all the electrons transmitted through the second storage grid 22. These collected electrons produce a current signal which is sent to a phase discriminator 44 over line 46, as more fully defined below. A deflection yoke 48, driven by suitable deflection circuitry 50, surrounds the tube 14 between the photo cathode 1'8 and storage grid 20, as well as a separate yoke between storage grids 20 and 22 so as to provide deflection and nutation of full image electron streams passing through these portions of the tube as well as displacement to match, as selectively desired. Suitable voltage control circuitry 52 is provided to individually control the voltage potentials to the multipliers 33, the accelerator grid 32, to each of the screens 20 and 22, and to the output anode 42, as desired either automatically or manually, and which control is necessary to the operation of the tube as more fully described below.

In operation reference image information either coming in as electrical video signels 36, or an optical input image 40 is written on the second grid 22 while maintaining the first grid 20 at a potential, by means of the voltage control circuitry 52, that renders it essentially transparent to the electron beam pasing down the tube from either of the input image sources. However, to eliminate as much distortion as possible, and to be sure comparison for correlation is made on an image with similar distortion, the reference image may first be written on the grid 20, and then transferred by the flood beam shown in FIGURE 3 to the second grid 22. Subsequent sensor data representing present image information is then written on the first storage grid after an adjustment of electrode potentials by the circuitry 52 and erasure on the first grid 20. For example, to Write first on grid 22, the grid may be at a potential of +524 volts with grid 20 at a potential of +14 volts. With storage then accomplished on grid 22, the potential of grid 20 may be adjusted to about +510 volts with grid 22 potential adjusted to +14 volts. This assumes the photo cathode 18 is at about potential. For correlation the potential on grid 20 will be about volts and grid 22 about volts.

In order to correlate the two resulting stored charge patterns, namely the present image stored on grid 20 and the reference image stored on grid 22, the first grid 20 is flooded with a total electron stream produced by a total coverage of lens 38 with a light source as shown in FIGURE 3. A total flood with the electron gun does not become practical even when the gun is centrally mounted as shown in FIGURE 2.

The total flood may be achieved in the embodiment of FIGURE 2 by mounting a ring shaped ultra-violet radiation source 19A in front of the area cathode 18A, and controlling actuation thereof by the voltage control circuitry 52A. With the area cathode 1 8A made very thin so as to be activated by the ultra-violet radiation, a total flood of electrons will be directed down the tube whenever the ultra-violet is actuated.

The charged grid 20 effectively space modulates the flood meam of electrons producing an electron image which is representative of the image stored thereon, and which is guided towards the grid 22 by the magnetic field produced by the focus coil 30. The charge pattern on the second storage screen 22 again space modulates the electron flow, permitting electrons to pass through the grid 22 only at those places Where a signal had not previously written a charge as an element of the reference pattern. The electronic image coming from the first storage grid is also nutated by yoke 48 during this period of time so as to achive a correlation for an automatic registration with the reference pattern on the second storage grid 22. Registration or correlation of the patterns is indicated by a maximum or minimum in the output signal picked up by anode 42. A maximum or minimum signal will depend on whether positives, negatives, or a combination of the two are stored and compared. This output signal is proportional to the product of the two images or charge patterns, and is defined as the correlation function.

The actual detection of the correlation output from anode 42 is achieved by the phase discriminator 44 which operates in conjunction with an integrator 54 to produce X and Y error signals which may be used to correct an aircraft flight path, or for any other well known control purpose for which the apparatus is utilized. With these error signals returned to the deflection circuitry 50 a closed loop system is achieved which immediately tends to correct any errors which may exist. The phase discriminator 44 operates in conjunction With a mutation generator 56 to determine, properly, the relative relationship between the reference and present image information in accordance with the current signal received by the output anode 42 so that the error signals X and Y are drawn to a proper reference.

FIGURE 2 illustrates a modified form of the invention which has the suflix A on all components corresponding to FIGURE 1. This is a completely electronic set up that cannot receive an optical image, but only an electronic signal to drive a gun 34A. Thus, an area cathode 18A replaces the photo cathode 18 of FIGURE 1, but is used only for total electron flood purposes. The cathode 18A has a central aperture 19 which allows transmission of a high resolution pencil type electron beam from the gun 34A for writing onto the grids 20A and 22A. Total uniform flooding to achieve correlation as described above is accomplished by the ultra-violet source 19A illuminating the area cathode :18A.

Thus, it is seen that the objects of the invention have been achieved by providing two storage screens in parallel which provides an additional flexibility to an image storage and correlation tube. The inclusion of the second storage grid between the photo cathode and the anode increases the usefulness of the device by providing the capability of receiving, storing, and area correlating two sets of segmented data such as that received from radar, IR, or microwave thermal sensors, as well as from a flying spot scanner. This arrangement may then be used to correlate area displays generated by sensors in incremental time sequence, displays generated as an image from an optical sensor, or any combination of these displays. It also makes possible an area correlation guidance system in which the reference data may be read into the correlator electrically either before or after launch of the vehicle. In other words, it eliminates the necessity for carrying stored reference information thereby providing considerable flexibility and usefulness to this particular apparatus. It also permits storage in real time of sequentially-received video information, the subsequent separate storage in real time of new sensor data, and the area correlation of the two stored images.

What is claimed is:

1. In an electron image storage tube the combination of an elongated tubular-shaped envelope,

a pair of flat electron image storage grids mounted in spaced parallel relation within the housing,

means to direct a stream of electrons representing image information into the housing and substantially perpendicularly towards the plane of the storage grids,

a thin area cathode activated by ultra-violet radiation mounted parallel to the storage grids,

an ultra-violet radiation source adjacent the cathode between the cathode and the grids,

means to flood the first grid closest to the cathode with a constant stream of electrons after images have been stored on each grid by actuating the ultraviolet radiation source to impinge ultra-violet radiation onto the cathode, whereby the first grid modulates the stream as it passes there through to produce an electron image of the information stored on the first grid,

means to nutate the modulated stream of electrons between the storage grids, and

means to detect the number of electrons of the mutated electron stream passing through the other storage grid which provides a correlation function between the images stored on the storage grids.

2. A tube according to claim 1 which includes a focus coil to selectively focus the electron image on either of the storage grids.

3. A tube according to claim 1 Where the means to direct a stream of electrons is an electron gun driven by a electronic input image.

4. A tube according to claim 1 Where the means to direct a stream of electrons includes an electron gun actuated by an electronic input image.

5. A tube according to claim 4 'Where the means to detect the number of electrons passing through the other storage screen is an anode in spaced parallel relation to said other screen and on the opposite end of the housing as the cathode and electron gun.

6. A tube according to claim 5 which includes electronic amplifier means between the anode and the other storage grid.

7. A tube according to claim 1 where the correlation function produces error signals which are used to deflect the nutated modulated stream of electrons so as to correct errors in the image information being correlated thereby providing a closed loop system.

8. A tube according to claim 1 which includes accelerator grids positioned selectively in the envelope to control the acceleration of electrons down the tube to and from the storage grids.

References Cited RODNEY D. BENNETT, Primary Examiner M. F. HUBLER, Assistant Examiner US. Cl. X.R. 

